I had never had much success with popovers or Yorkshire puds - they never popped for me. Until I read a recipe that mentioned that the consistency of the batter should be like thick cream. All of the recipes, like the one posted above, call for the same volume of flour as for milk. In my arid climate, that results in a thick batter like for pancakes, which is wayyyyy to thick for popovers. Now, I add 25-30% extra liquid, and I get nice high puffy popovers.

Note that weighing the flour instead of using volume measures doesn't work either - my flour will always contain more flour and less moisture, regardless of how it is measured.